Abstract:

Claims:

1. An aqueous binder for fibrous and/or granular substrates comprisinga)
an addition polymer A obtained by free-radical polymerization of0.1% to
40% by weight of at least one C3 to C30 alkene (monomer A1),40% to 99.9%
by weight of at least one ethylenically unsaturated C3 to C6
monocarboxylic acid (monomer A2),0% to 50% by weight of at least one
ethylenically unsaturated C4 to C12 dicarboxylic acid and/or of the
ethylenically unsaturated dicarboxylic monoalkyl esters or dicarboxylic
anhydrides obtainable from said acid (monomer A3), and0% to 30% by weight
of at least one other ethylenically unsaturated compound which is
copolymerizable with the monomers A1 to A3 (monomer A4),the monomers A1
to A4 adding up to 100% by weight, andb) a polyol compound having at
least 2 hydroxyl groups (polyol B).

2. The binder according to claim 1, the weight ratio of polymer A to
polyol B being 1:10 to 100:1.

3. The binder according to claim 1, the polymer A having been obtained by
free-radical polymerization of1% to 25% by weight of monomers A 1,50% to
89% by weight of monomers A2, and10% to 40% by weight of monomers A3.

4. The binder according to claim 1, the monomers A1 being selected from
1-alkenes having 6 to 18 carbon atoms.

11. The binder according to claim 1, the amounts of polymer A and polyol B
being chosen so that the ratio of the number of equivalents of carboxyl
groups of the polymer A to the number of equivalents of hydroxyl groups
of the polyol B is 100:1 to 1:3.

12. An addition polymer A obtained by free-radical polymerization of0.1%
to 40% by weight of at least one C3 to C30 alkene (monomer A 1),40% to
99.9% by weight of at least one ethylenically unsaturated C3 to C6
monocarboxylic acid (monomer A2),0% to 50% by weight of at least one
ethylenically unsaturated C4 to C12 dicarboxylic acid and/or of the
ethylenically unsaturated dicarboxylic monoalkyl esters or dicarboxylic
anhydrides obtainable from said acid (monomer A3), and0% to 30% by weight
of at least one other ethylenically unsaturated compound which is
copolymerizable with the monomers A 1 to A3 (monomer A4),the monomers A 1
to A4 adding up to 100% by weight.

13. An aqueous binder comprising0.1% to 40% by weight of at least one C3
to C30 alkene (monomer A 1),40% to 99.9% by weight of at least one
ethylenically unsaturated C3 to C6 monocarboxylic acid (monomer A2),0% to
50% by weight of at least one ethylenically unsaturated C4 to C12
dicarboxylic acid and/or of the ethylenically unsaturated dicarboxylic
monoalkyl esters or dicarboxylic anhydrides obtainable from said acid
(monomer A3), and0% to 30% by weight of at least one other ethylenically
unsaturated compound which is copolymerizable with the monomers A1 to A3
(monomer A4),the monomers A1 to A4 adding up to 100% by weight, andb) a
polyol compound having at least 2 hydroxyl groups (polyol B).

14. A process for producing a shaped article from a fibrous and/or
granular substrate and an aqueous binder, which comprises first
impregnating the fibrous and/or granular substrate with an aqueous binder
according to claim 13, bringing the impregnated substrate, optionally,
into the desired shape, and subsequently drying the impregnated substrate
and curing it at a temperature ≧130.degree. C.

15. The process according to claim 14, wherein the amount of aqueous
binder is chosen so that ≧1 g and ≦100 g of binder, formed
from the sum of polymer A and polyol B (calculated as solid), are used
per 100 g of fibrous and/or granular substrate.

16. A shaped article obtainable by a process according to claim 14.

Description:

[0001]The subject matter of the present invention relates to the use of an
aqueous binder comprising

a) an addition polymer A obtained by free-radical polymerization of
[0002]0.1% to 40% by weight of at least one C3 to C30 alkene (monomer
A1), [0003]40% to 99.9% by weight of at least one ethylenically
unsaturated C3 to C6 monocarboxylic acid (monomer A2), [0004]0% to 50% by
weight of at least one ethylenically unsaturated C4 to C12 dicarboxylic
acid and/or of the ethylenically unsaturated dicarboxylic monoalkyl
esters or dicarboxylic anhydrides obtainable from said acid (monomer A3),
and [0005]0% to 30% by weight of at least one other ethylenically
unsaturated compound which is copolymerizable with the monomers A1 to A3
(monomer A4), [0006]the monomers A1 to A4 adding up to 100% by weight
(total monomer amount), and

[0007]b) a polyol compound having at least 2 hydroxyl groups (polyol B) as
a binder for fibrous and/or granular substrates.

[0008]Subject matter of the present invention is likewise a process for
producing shaped articles using fibrous or granular substrates and
aqueous binder, and also the shaped articles themselves.

[0009]The consolidation of fibrous or granular substrates, more
particularly in sheetlike structures, exemplified by fiber webs,
fiberboard or chipboard panels, etc, is frequently accomplished
chemically using a polymeric binder. To increase the strength,
particularly the wet strength and thermal stability, in many cases
binders are used which comprise crosslinkers that give off formaldehyde.
As a consequence of this, however, there is a risk of unwanted
formaldehyde emission.

[0010]For the purpose of avoiding formaldehyde emissions there have
already been numerous alternatives proposed to the binders known to date.
For instance U.S. Pat. No. 4,076,917 discloses binders which comprise
carboxylic acid-containing or carboxylic anhydride-containing polymers
and 6-hydroxyalkylamide crosslinkers. A disadvantage is the relatively
costly and inconvenient preparation of the 13-hydroxyalkylamides.

[0011]EP-A-445578 discloses boards made of finely divided materials, such
as glass fibers, for example, in which mixtures of high molecular weight
polycarboxylic acids and polyhydric alcohols, alkanolamines, or
polyfunctional amines act as binders.

[0012]EP-A 583086 discloses formaldehyde-free aqueous binders for
producing fiber webs, more particularly glass fiber webs. The binders
comprise a polycarboxylic acid having at least two carboxylic acid groups
and also, if appropriate, anhydride groups, and a polyol. These binders
require a phosphorus reaction accelerant in order to attain sufficient
strengths on the part of the glass fiber webs. It is noted that the
presence of such a reaction accelerant is vital unless a highly reactive
polyol is used. Highly reactive polyols specified include
β-hydroxyalkylamides.

[0014]EP-A 672920 describes formaldehyde-free binding, impregnating or
coating compositions which comprise at least one polyol and a polymer
which is composed to an extent of 2% to 100% by weight of an
ethylenically unsaturated acid or acid anhydride comonomer. The polyols
are substituted triazine, triazinetrione, benzene or cyclohexyl
derivatives, and the polyol radicals are always located in positions 1,
3, and 5 of the aforementioned rings. In spite of a high drying
temperature, the wet tensile strengths obtained with these binders on
glass fiber webs are low.

[0015]DE-A 2214450 describes a copolymer composed of 80% to 99% by weight
of ethylene and 1% to 20% by weight of maleic anhydride. Together with a
crosslinking agent, the copolymer is used in powder form or in dispersion
in an aqueous medium for the purpose of surface coating. The crosslinking
agent used is a polyalcohol which contains amino groups. In order to
bring about crosslinking, however, heating must be carried out at up to
300° C.

[0016]U.S. Pat. No. 5,143,582 discloses the production of heat-resistant
nonwoven-web materials using a thermosetting heat-resistant binder. The
binder is formaldehyde-free and is obtained by mixing a crosslinker with
a polymer containing carboxylic acid groups, carboxylic anhydride groups
or carboxylic salt groups. The crosslinker is a β-hydroxy-alkylamide
or a polymer or copolymer thereof. The polymer crosslinkable with the
β-hydroxyalkylamide is synthesized, for example, from unsaturated
monocarboxylic or dicarboxylic acids, salts of unsaturated monocarboxylic
or dicarboxylic acids, or unsaturated anhydrides. Self-curing polymers
are obtained by copolymerizing the β-hydroxyalkylamides with
monomers comprising carboxyl groups.

[0017]Processes for preparing addition polymers based on alkenes and other
copolymerizable ethylenically unsaturated compounds are well known to the
skilled worker. The copolymerization takes place essentially in the form
of a solution polymerization (see, for example, A. Sen et al., Journal
American Chemical Society, 2001, 123, pages 12 738 to 12 739; B.
Klumperman et al., Macromolecules, 2004, 37, pages 4406 to 4416; A. Sen
et al., Journal of Polymer Science, Part A: Polymer Chemistry, 2004,
42(24), pages 6175 to 6192; WO 03/042254, WO 03/091297 or EP-A 1384729)
or in the form of an aqueous emulsion polymerization, this taking place
more particularly on the basis of the lowest alkene, ethene (see, for
example, U.S. Pat. No. 4,921,898, U.S. Pat. No. 5,070,134, U.S. Pat. No.
5,110,856, U.S. Pat. No. 5,629,370, EP-A 295727, EP-A 757065, EP-A
1114833 or DE-A 19620817).

[0019]DE-A 1720277 discloses a process for preparing film-forming aqueous
polymer dispersions using vinyl esters and 1-octene. The weight ratio of
vinyl ester to 1-octene can be from 99:1 to 70:30. Optionally the vinyl
esters can be used to a minor extent in a mixture with other
copolymerizable ethylenically unsaturated compounds for the emulsion
polymerization.

[0020]S. M. Samoilov in J. Macromol. Sci. Chem., 1983, A19(1), pages 107
to 122 describes the free-radically initiated aqueous emulsion
polymerization of propene with different ethylenically unsaturated
compounds. The outcome observed there was that the copolymerization of
propene with ethylenically unsaturated compounds having strongly
electron-withdrawing groups, such as chlorotrifluoroethylene,
trifluoroacrylonitrile, maleic anhydride or methyl trifluoroacrylate,
gave polymers having a markedly higher propene fraction, or copolymers
having higher molecular weights, than when using the ethylenically
unsaturated compounds typically associated with free-radically initiated
aqueous emulsion polymerization, viz. vinyl acetate, vinyl chloride,
methyl acrylate and/or butyl acrylate. The reasons given for this
behavior include more particularly the hydrogen radical transfer
reactions that are typical of the higher alkenes.

[0021]The preparation of aqueous polymer dispersions based on different,
extremely water-insoluble monomers by free-radically initiated emulsion
polymerization using host compounds is disclosed in U.S. Pat. No.
5,521,266 and EP-A 780401.

[0022]DE-A 102005035692 discloses the preparation of aqueous polymer
dispersions based on alkenes having 5 to 12 C atoms. The alkenes having 5
to 12 C atoms are metered into the polymerization mixture under
polymerization conditions.

[0023]EP-A 891430 discloses aqueous polymer systems for imparting water
repellency to leather, said systems being obtained by free-radical
polymerization of 20% to 90% by weight of monoethylenically unsaturated
C4 to C6 dicarboxylic acids and/or their anhydrides with 5% to 50% by
weight of a C2 to C6 olefin and 5% to 50% by weight of a hydrophobic
ethylenically unsaturated monomer.

[0024]EP-A 670909 discloses aqueous polymer dispersions which are used as
a component for fatliquoring or softening leather and which are obtained
by free-radical polymerization of maleic anhydride, C12 to C30
α-olefins, and esters of acrylic acid, methacrylic acid and/or
maleic acid with C12 to C30 alcohols.

[0025]Coating compositions based on a crosslinker, such as an
endgroup-capped polyisocyanate or an amino resin, for example, and on an
emulsion polymer based on α-olefins and ethylenically unsaturated
carboxylic anhydrides, are disclosed in EP-A 450-452.

[0027]It was an object of the present invention to provide an alternative
formaldehyde-free binder system for fibrous or granular substrates.

[0028]The use defined at the outset has accordingly been found.

[0029]In accordance with the invention an aqueous binder is used that
comprises an addition polymer A obtained by free-radical polymerization
of

0.1% to 40% by weight of at least one monomer A1,40% to 99.9% by weight of
at least one monomer A2,0% to 50% by weight of at least one monomer A3,
and0% to 30% by weight of at least one monomer A4.

[0030]With particular advantage, aqueous binders are used which comprise
an addition polymer A obtained by free-radical polymerization of

1% to 25% by weight of at least one monomer A1,50% to 89% by weight of at
least one monomer A2, and10% to 40% by weight of at least one monomer
A3,and with particular advantage4% to 20% by weight of at least one
monomer A1,55% to 70% by weight of at least one monomer A2, and20% to 35%
by weight of at least one monomer A3.

[0032]Preference is given to using the 1-alkenes, examples being propene,
2-methylpropene, but-1-ene, pent-1-ene, hex-1-ene, hept-1-ene, oct-1-ene,
non-1-ene, dec-1-ene, undec-1-ene, dodec-1-ene,
2,4,4-trimethylpent-1-ene, 2,4-dimethylhex-1-ene, 6,6-dimethylhept-1-ene,
2-methyloct-1-ene, tridec-1-ene, tetradec-1-ene, hexadec-1-ene,
heptadec-1-ene, octadec-1-ene, nonadec-1-ene, eicos-1-ene, docos-1-ene,
tetracos-1-ene, 2,6-dimethyldodec-1-ene, 6-butyldec-1-ene,
4,8,12-trimethyldec-1-ene or 2-methylheptadec-1-ene. Advantageously, at
least one monomer A1 used is an alkene having 6 to 18 carbon atoms,
preferably a 1-alkene having 8 to 12 carbon atoms. Preference is given
more particularly to using oct-1-ene, non-1-ene, dec-1-ene, undec-1-ene
and/or dodec-1-ene, with oct-1-ene and dodec-1-ene being particularly
preferred.

[0033]The amount of monomers A1 in the preparation of the polymer A is
0.1% to 40%, preferably 1% to 25%, and with more particular preference 4%
to 20% by weight, based in each case on the total monomer amount.

[0034]Monomers A2 contemplated are ethylenically unsaturated
monocarboxylic acids, more particularly α,β-monoethylenically
unsaturated monocarboxylic acids, of 3 to 6 carbon atoms, and also their
water-soluble salts, more particularly their alkali metal salts or
ammonium salts, such as, for example, acrylic acid, methacrylic acid,
ethyl acrylic acid, allyl acetic acid, crotonic acid and/or vinyl acetic
acid, and also the ammonium, sodium or potassium salts of the
aforementioned acids. Particularly preference is given to acrylic acid
and methacrylic acid, with acrylic acid being more particularly
preferred.

[0035]The amount of monomers A2 in the preparation of the polymer A is 40%
to 99.9%, preferably 50% to 89%, and with more particular preference 55%
to 70% by weight, based in each case on the total monomer amount.

[0037]The amount of monomers A3 in the preparation of the polymer A is 0%
to 50%, preferably 10% to 40%, and with more particular preference 20% to
35% by weight, based in each case on the total monomer amount.

[0038]Monomers A4 contemplated are all those ethylenically unsaturated
compounds which can easily be copolymerized free-radically with the
monomers A1 to A3, such as, for example, vinylaromatic monomers, such as
styrene, α-methylstyrene, o-chlorostyrene or vinyltoluenes, vinyl
halides, such as vinyl chloride or vinylidene chloride, esters of vinyl
alcohol and monocarboxylic acids having 1 to 18 C atoms, such as vinyl
acetate, vinyl propionate, vinyl n-butyrate, vinyl laurate, and vinyl
stearate, esters of α,β-monoethylenically unsaturated
monocarboxylic and dicarboxylic acids preferably of 3 to 6 C atoms, such
as, more particularly, acrylic acid, methacrylic acid, maleic acid,
fumaric acid, and itaconic acid, with alkanols having generally 1 to 12,
preferably 1 to 8, and more particularly 1 to 4 C atoms, such as, in
particular, methyl, ethyl, n-butyl, isobutyl, pentyl, hexyl, heptyl,
octyl, nonyl, decyl and 2-ethylhexyl acrylate and methacrylate, dimethyl
or di-n-butyl fumarate and maleate, nitriles of
α,β-monoethylenically unsaturated carboxylic acids, such as
acrylonitrile, methacrylonitrile, fumaronitrile, maleonitrile, and also
C4-8 conjugated dienes, such as 1,3-butadiene (butadiene) and
isoprene. The stated monomers generally form the principal monomers,
which, based on the total amount of monomers A4, account for a fraction
of ≧50%, preferably ≧80%, and with more particular
preference ≧90% by weight, or even form the total amount of the
monomers A4. As a general rule these monomers are of only moderate to low
solubility in water under standard conditions [20° C., 1 atm
(absolute)].

[0039]Monomers A4 which have a heightened water-solubility under the
above-stated conditions are those which comprise either at least one
sulfonic acid group and/or its corresponding anion, or at least one
amino, amido, ureido or N-heterocyclic group and/or the ammonium
derivatives thereof that are alkylated or protonated on the nitrogen.
Mention may be made exemplarily of acrylamide and methacrylamide, and
also vinylsulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid,
styrenesulfonic acid, and their water-soluble salts, and also
N-vinylpyrrolidone, 2-vinylpyridine, 4-vinylpyridine, 2-vinylimidazole,
2-(N,N-dimethylamino)ethyl acrylate, 2-(N,N-dimethylamino)ethyl
methacrylate, 2-(N,N-diethylamino)ethyl acrylate,
2-(N,N-diethylamino)ethyl methacrylate, 2-(N-tert-butylamino)ethyl
methacrylate, N-(3-N',N'-dimethylaminopropyl)methacrylamide, and
2-(1-imidazoline-2-onyl)ethyl methacrylate. Normally the aforementioned
water-soluble monomers A4 are used only as modifying monomers, in amounts
of ≧10%, preferably ≧5%, and with more particular
preference ≧3% by weight, based in each case on the total amount
of monomers A4.

[0040]Monomers A4 which typically enhance the internal strength of the
films formed from a polymer matrix normally contain at least one epoxy
group, at least one carbonyl group or at least two nonconjugated
ethylenically unsaturated double bonds. Examples of such monomers are
monomers containing two vinyl radicals, monomers containing two
vinylidene radicals, and monomers containing two alkenyl radicals.
Particularly advantageous in this context are the diesters of dihydric
alcohols with α,β-monoethylenically unsaturated monocarboxylic
acids, among which acrylic acid and methacrylic acid are preferred.
Examples of such monomers containing two nonconjugated ethylenically
unsaturated double bonds are alkylene glycol diacrylates and
dimethacrylates, such as ethylene glycol diacrylate, 1,2-propylene glycol
diacrylate, 1,3-propylene glycol diacrylate, 1,3-butylene glycol
diacrylate, 1,4-butylene glycol diacrylates, and ethylene glycol
dimethacrylate, 1,2-propylene glycol dimethacrylate, 1,3-propylene glycol
dimethacrylate, 1,3-butylene glycol dimethacrylate, and 1,4-butylene
glycol dimethacrylate, and also divinylbenzene, vinyl methacrylate, vinyl
acrylate, allyl methacrylate, allyl acrylate, diallyl maleate, diallyl
fumarate, methylenebisacrylamide, cyclopentadienyl acrylate, triallyl
cyanurate or triallyl isocyanurate. Frequently the aforementioned
crosslinking monomers A4 are used in amounts of ≧10% by weight,
but preferably in amounts of ≧3% by weight, based in each case on
the total amount of monomers A4. With more particular preference,
however, no such crosslinking monomers A4 at all are used in preparing
the polymer A.

[0041]Advantageously, for the purpose of preparing the polymer A, monomers
A4 used are those monomers or monomer mixtures which comprise [0042]50%
to 100% by weight of esters of acrylic and/or methacrylic acid with
alkanols containing 1 to 12 carbon atoms, or [0043]50% to 100% by weight
of styrene and/or butadiene, or [0044]50% to 100% by weight of vinyl
chloride and/or vinylidene chloride, or [0045]50% to 100% by weight of
vinyl acetate and/or vinyl propionate.

[0046]The amount of monomers A4 in the preparation of the polymer A is 0%
to 30% by weight and preferably 0% to 15%, based in each case on the
total monomer amount. With more particular preference no monomers A4 are
used.

[0047]In accordance with the invention it is optionally possible to
include in each case a portion or the total amount of the monomers A1 to
A4 in the initial charge to the polymerization vessel. It is also
possible, however, in each case to meter in optionally the total amount
or the respective remainder, of the monomers A1 to A4 during the
polymerization reaction. The total amounts or the optionally remainders,
of monomers A1 to A4 may in that case be metered discontinuously, in one
or more portions, or continuously, with constant or changing volume
flows, to the polymerization vessel. Frequently at least a portion of the
monomers A1 and/or A3, and, advantageously, monomer A3 exclusively, in
the polymerization medium, is included in the initial charge before the
polymerization reaction is initiated.

[0048]The preparation of the polymers A is familiar in principle to the
skilled worker and is accomplished more particularly by means of
free-radically initiated solution polymerization, in water, for example,
or in an organic solvent (see, for example, A. Echte, Handbuch der
Technischen Polymerchemie, chapter 6, VCH, Weinheim, 1993 or B. Vollmert,
Grundriss der Makromolekularen Chemie, volume 1, E. Vollmert Verlag,
Karlsruhe, 1988).

[0050]Preference, however, is given to selecting those aprotic organic
solvents in which the particular free-radical initiators used dissolve
well. More particularly, use is made of those aprotic organic solvents in
which not only the free-radical initiators but also the polymers A
dissolve well. More particular preference is given to selecting those
aprotic organic solvents which additionally can be separated in a simple
way from the resulting polymer A solution, such as, for example, by
distillation, inert-gas stripping and/or steam distillation. Preferred
examples of such are esters of aliphatic C1 to C5 carboxylic acids or
aromatic carboxylic acids with aliphatic C1 to C5 alcohols, such as ethyl
formate, n-propyl formate, isopropyl formate, n-butyl formate, isobutyl
formate, tert-butyl formate, amyl formate, methyl acetate, ethyl acetate,
n-propyl acetate, isopropyl acetate, n-butyl acetate, isobutyl acetate,
tert-butyl acetate, amyl acetate, methyl propionate, ethyl propionate,
n-propyl propionate, isopropyl propionate, n-butyl propionate, isobutyl
propionate, tert-butyl propionate, amyl propionate, methyl butyrate,
ethyl butyrate, n-propyl butyrate, isopropyl butyrate, linear or cyclic
aliphatic ethers, such as diisopropyl ether, 1,3- or 1,4-dioxane,
tetrahydrofurane or ethylene glycol dimethyl ether, methyl glycol
acetate, diethyl carbonate, linear or cyclic aliphatic C3 to C7 ketones,
such as acetone, methyl ethyl ketone, methyl isobutyl ketone, 2- or
3-hexanone, 2-, 3- or 4-heptanone, cyclopentanone, or cyclohexanone.
Particularly preferred solvents are the abovementioned esters of
aliphatic C1 to C5 carboxylic acids or aromatic carboxylic acids with
aliphatic C1 to C5 alcohols, but more particularly ethyl acetate and
ethyl butyrate, and also C4 to C6 ketones, more particularly methyl ethyl
ketone. It is advantageous if the solvent has a boiling point under
atmospheric pressure (1 atm=1.013 bar) ≦140° C., frequently
≦125° C., and more particularly ≦100° C., or
forms a low-boiling azeotropic water/solvent mixture with water. It will
be appreciated that a mixture of two or more solvents can also be used.

[0051]The amount of solvent in the preparation of the polymer A is 40 to
9900 parts, preferably 70 to 400 parts, and with more particular
preference 80 to 200 parts by weight, based in each case on 100 parts by
weight of total monomers.

[0052]In accordance with the invention it is optionally possible to
include a portion or the entirety of solvent in the initial charge to the
polymerization vessel. It is, however, also possible to meter in the
entirety or any remainder of solvent during the polymerization reaction.
In that case the entirety or the optional remainder of solvent can be
metered into the polymerization vessel discontinuously, in one or more
portions, or continuously, with constant or changing volume flows.
Advantageously a portion of the solvent as polymerization medium is
included in the initial charge to the polymerization vessel before the
polymerization reaction is initiated, and the remainder is metered in
together with the monomers A1 to A4 and the free-radical initiator during
the polymerization reaction.

[0053]The free-radical polymerization of the monomers A1 to A4 is
initiated and maintained by means of what are known as free-radical
initiators. Free-radical initiators (initiators which form free radicals)
that are suitable are preferably all those radical-forming initiators
which have a half-life at polymerization temperature of ≧4 hours,
more particularly ≧1 hour, and advantageously ≧30 minutes.

[0054]Where the polymerization of the monomers A1 to A4 is carried out in
an aqueous medium, use is made of what are known as water-soluble
free-radical initiators, which the skilled worker typically uses in the
case of free-radically initiated aqueous emulsion polymerization. If, on
the other hand, the polymerization of the monomers is carried out in an
organic solvent, then what are known as oil-soluble free-radical
initiators are used, which the skilled worker typically uses in the case
of free-radically initiated solution polymerization.

[0057]The amount of free-radical initiator used is generally 0.01% to 10%,
preferably 0.1% to 8%, and with more particular preference 1% to 6% by
weight, based in each case on the total monomer amount.

[0058]In accordance with the invention it is optionally possible to
include a portion or the entirety of free-radical initiator in the
initial charge to the polymerization vessel. It is also possible,
however, to meter in the entirety or the optional remainder of
free-radical initiator during the polymerization reaction. The entirety
or the remainder of free-radical initiator may in that case be optionally
metered into the polymerization vessel discontinuously, in one or more
portions, or continuously, with constant or changing volume flows. With
more particular advantage the free-radical initiator is metered during
the polymerization reaction continuously, with constant volume flow--more
particularly in the form of a solution of the free-radical initiator with
the solvent used.

[0059]Polymer A advantageously has a weight-average molecular weight
≧1000 g/mol and ≦100 000 g/mol. It is advantageous if the
weight-average molecular weight of polymer A is ≦50 000 g/mol or
≦40 000 g/mol. With more particular advantage polymer A has a
weight-average molecular weight ≧3000 g/mol and ≦40 000
g/mol. With particular advantage the weight-average molecular weight is
situated in the range ≧3000 and ≦25 000 g/mol. The setting
of the weight-average molecular weight during the preparation of polymer
A is familiar to the skilled worker and is advantageously accomplished by
free-radically initiated aqueous solution polymerization in the presence
of free-radical chain-transfer compounds, referred to as free-radical
chain regulators. The determination of the weight-average molecular
weight is also familiar to the skilled worker and is accomplished, for
example, by means of gel permeation chromatography.

[0060]Examples of suitable free-radical chain regulators are organic
compounds comprising sulfur in bonded form. They include, for example,
mercapto compounds, such as mercaptoethanol, mercaptopropanol,
mercaptobutanol, mercaptoacetic acid, mercaptopropionic acid, butyl
mercaptan, and dodecyl mercaptan. Further free-radical chain regulators
are familiar to the skilled worker. If the polymerization is carried out
in the presence of free-radical chain regulators, it is common to use
0.01% to 10% by weight, based on the total monomer amount.

[0061]In accordance with the invention it is possible to include at least
a portion of the free-radical chain regulator in the initial charge to
the polymerization medium and to add the optional remainder to the
polymerization medium after the free-radical polymerization reaction has
been initiated, that addition taking place discontinuously in one
portion, discontinuously in two or more portions, and also continuously
with constant or changing volume flows. Frequently the total amount of
the free-radical chain regulator is added continuously, together with the
monomers A1 to A4, during the polymerization reaction.

[0062]By controlled variation of the nature and amount of the monomers A1
to A4 it is possible in accordance with the invention for the skilled
worker to prepare polymers A which have a glass transition temperature or
a melting point in the range from -60 to 270° C. Advantageously in
accordance with the invention the glass transition temperature of the
polymer A is ≧-20° C. and ≦110° C., and
preferably ≧20° C. and ≦105° C.

where x1, x2, . . . xn are the mass fractions of the
monomers 1, 2, . . . n and Tgn, Tg2, . . .
Tgn are the glass transition temperatures of the polymers
synthesized in each case only from one of the monomers 1, 2, . . . n, in
degrees Kelvin. The Tg values for the homopolymers of the majority
of monomers are known and are listed, for example, in Ullmann's
Encyclopedia of Industrial Chemistry, 5th edition, vol. A21, page 169,
VCH Weinheim, 1992; further sources of homopolymer glass transition
temperatures include, for example, J. Brandrup, E. H. Immergut, Polymer
Handbook, 1st ed., J. Wiley, New York 1966, 2nd ed. J. Wiley, New York
1975, and 3rd ed. J. Wiley, New York 1989).

[0065]The polymer A solutions obtained in accordance with the invention
typically have polymer solids contents of ≧10% and ≦70%,
frequently ≧20% and ≦65%, and often 40% and ≦60% by
weight, based in each case on the corresponding polymer A solution.

[0066]Depending on the free-radical initiator used, the free-radically
initiated polymerization takes place typically at temperatures in the
range from 40 to 180° C., preferably from 50 to 150° C.,
and more particularly from 60 to 110° C. As soon as the
temperature during the polymerization reaction is above the boiling point
of the solvent and/or of one of the monomers A1 to A4, the polymerization
is carried out advantageously under pressure (>1 atm absolute). The
temperature and pressure conditions are familiar to the skilled worker or
can be determined by him or her in a few routine experiments.

[0067]The polymers A can be prepared in the typical polymerization
devices. Examples of those used for this purpose include glass flasks
(laboratory) or stirred tanks (industrial scale) equipped with an anchor,
blade, impeller, cross-arm, MIG or multistage pulsed counter-current
stirrer. In the case more particularly of polymerization in the presence
of only small amounts of solvent, it may also be advantageous to carry
out the polymerization in typical one-screw of two-screw (co-rotating or
counter-rotating) kneader reactors, such as those, for example, from the
company List or Buss SMS.

[0068]Where polymer A is prepared in an organic solvent, at least some of
the organic solvent, advantageously ≧50% or ≧90% by weight,
and, with more particular advantage, all of the organic solvent, is
generally removed, and the polymer A is taken up in water, advantageously
in deionized water. The corresponding methods are familiar to the skilled
worker. Thus, for example, the switching of the solvent for water can be
accomplished by distilling off at least some of the solvent,
advantageously all of it, in one or more stages, at, for example,
atmospheric pressure (1 atm absolute) or subatmospheric pressure (<1
atm absolute), and replacing it by water. Frequently it may be
advantageous to remove the solvent from the solution by introducing steam
and at the same time to replace it by water. This is more particularly
the case when the organic solvent has a certain steam volatility.

[0069]Also comprised in accordance with the invention, therefore, is an
addition polymer A obtainable by free-radical polymerization of

0.1% to 40% by weight of at least one monomer A1,40% to 99.9% by weight of
at least one monomer A2,0% to 50% by weight of at least one monomer A3,
and0% to 30% by weight of at least one monomer A4,the monomers A1 to A4
adding up to 100% by weight.

[0070]Likewise comprised in accordance with the invention, therefore, is
an aqueous binder comprising

a) an addition polymer A obtained by free-radical polymerization of
[0071]0.1% to 40% by weight of at least one monomer A1, [0072]40% to
99.9% by weight of at least one monomer A2, [0073]0% to 50% by weight of
at least one monomer A3, and [0074]0% to 30% by weight of at least one
monomer A4,the monomers A1 to A4 adding up to 100% by weight, andb) a
polyol compound having at least 2 hydroxyl groups (polyol B).

[0075]The aqueous binder used in accordance with the invention comprises
not only the polymer A but also a polyol B which has at least 2 hydroxyl
groups. It is advantageous in this context to use those polyols B which
are not volatile at the temperatures of drying and/or curing and which
therefore have a correspondingly low vapor pressure.

[0076]The polyol B may in principle be a compound having a molecular
weight ≦1000 g/mol or a polymeric compound having a molecular
weight >1000 g/mol. Examples of polymeric compounds having at least 2
hydroxyl groups include polyvinyl alcohol, partly hydrolyzed polyvinyl
acetate, homopolymers or copolymers of hydroxyalkyl acrylates or
hydroxyalkyl methacrylates, such as hydroxyethyl acrylate or methacrylate
or hydroxypropyl acrylate or methacrylate, for example. Examples of
further polymeric polyols B are given in WO 97/45461, page 3, line 3 to
page 14, line 33, among other publications.

[0077]Compounds contemplated as polyol B with a molecular weight
≦1000 g/mol include all those organic compounds which have at
least 2 hydroxyl groups and a molecular weight ≦1000 g/mol.
Mention may be made exemplarily of ethylene glycol, 1,2-propylene glycol,
glycerol, 1,2- and 1,4-butanediol, pentaerythritol, trimethylolpropane,
sorbitol, sucrose, glucose, 1,2-, 1,3-, and 1,4-dihydroxybenzene,
1,2,3-trihydroxybenzene, 1,2-, 1,3-, and 1,4-dihydroxycyclohexane, and
also, preferably, alkanolamines, such as, for example compounds in the
general formula I

##STR00001##

in which R1 is an H atom, a C1-C10 alkyl group or a
C2-C10 hydroxyalkyl group, and R2 and R3 are a
C2-C10 hydroxyalkyl group.

[0078]With particular preference R2 and R3 independently of one
another are a C2-C5 hydroxyalkyl group, and R1 is an H
atom, a C1-C5 alkyl group or a C2-C5 hydroxyalkyl
group.

[0079]Compounds of the formula I include more particularly diethanolamine,
triethanolamine, diisopropanolamine, triisopropanolamine,
methyldiethanolamine, butyldiethanolamine and/or
methyldiisopropanolamine.

[0080]Examples of further polyols B having a molecular weight ≦1000
g/mol are likewise found in WO 97/45461, page 3, line 3 to page 14, line
33.

[0082]For the aqueous binders which can be used in accordance with the
invention, the polymer A and the polyol B are used preferably in a
quantitative ratio to one another such that the weight ratio of polymer A
to polyol B is 1:10 to 100:1, advantageously 1:5 to 50:1, and with more
particular advantage 1:1 to 10:1.

[0083]With more particular advantage the amounts of polymer A and polyol B
are chosen such that the ratio of the number of equivalents of carboxyl
groups of the polymer A to the number of equivalents of hydroxyl groups
of the polyol B is 100:1 to 1:3, preferably 50:1 to 1:2, and more
preferably 10:1 to 1:1 (the anhydride groups in this case being counted
as 2 carboxyl groups).

[0084]The preparation of the aqueous binders which can be used in
accordance with the invention is familiar to the skilled worker and is
accomplished, for example, in a simple way by addition of the polyol B to
the aqueous solution of the polymer A.

[0085]The aforementioned aqueous binders comprise preferably less than
1.5% by weight, more particularly less than 1.0%, more preferably less
than 0.5%, and very preferably less than 0.3%, more particularly less
than 0.1%, by weight, based on the sum of polymer A and polyol B
(solid/solid), of a phosphorus reaction accelerant. Phosphorus reaction
accelerants are disclosed in, for example, EP-A 583086 and EP-A 651088.
They include, more particularly, alkali metal hypophosphites, phosphites,
polyphosphates, and dihydrogen phosphates, polyphosphoric acid,
hypophosphoric acid, phosphoric acid, alkylphosphinic acid, or oligomers
and/or polymers of these salts and acids.

[0086]The aqueous binders preferably comprise no phosphorus reaction
accelerants or no amounts of a phosphorus compound that are active in
accelerating the reaction. The binders of the invention may, however,
comprise esterification catalysts familiar to the skilled worker, such
as, for example, sulfuric acid or p-toluenesulfonic acid, or titanates or
zirconates.

[0087]Furthermore, the aqueous binders of the invention may also comprise
further, optional auxiliaries familiar to the skilled worker, such as,
for example, what are known as thickeners, defoamers, neutralizing
agents, buffer substances, preservatives, finely divided inert fillers,
such as aluminum silicates, quartz, precipitated or fumed silica, light
or heavy spar, talc or dolomite, coloring pigments, such as titanium
white, zinc white or black iron oxide, adhesion promoters and/or flame
retardants.

[0088]Where the aqueous binders of the invention are to be used as binders
for mineral fibers and/or glass fibers or webs produced from them,
advantageously ≧0.001% and ≦5% by weight, and with more
particular advantage ≧0.05% and ≦2% by weight, based on the
total amount of polymer A and polyol B, of at least one silicon adhesion
promoter is added to the aqueous binders, some examples being an alkoxy
silane, such as methyltrimethoxysilane, n-propyltrimethoxysilane,
n-octyltrimethoxysilane, n-decyl-triethoxysilane,
n-hexadecyltrimethoxysilane, dimethyldimethoxysilane,
trimethyl-methoxysilane, 3-acetoxypropyltrimethoxysilane,
3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane,
3-chloropropyltrimethoxysilane, 3-glycidyloxypropyl-trimethoxysilane,
3-mercaptopropyltrimethoxysilane and/or phenyltrimethoxysilane, with
particular preference being given to functionalized alkoxy silanes, such
as 3-acetoxypropyltrimethoxysilane, 3-aminopropyltrimethoxysilane,
3-aminopropyl-triethoxysilan, 3-chloropropyl-trimethoxysilane,
3-glycidyloxypropyltrimethoxysilane and/or
3-mercaptopropyl-trimethoxysilane.

[0089]The aqueous binders which can be used in accordance with the
invention typically have solids contents (formed from the sum of polymer
A and polyol B reckoned as solids) of ≧5% and ≦70%,
frequently ≧10% and ≦65%, and often ≧15% and
≦55%, by weight, based in each case on the aqueous binder.

[0090]The aqueous binders which can be used in accordance with the
invention typically have pH values (measured at 23° C.; diluted
with deionized water to a solids content of 10% by weight) in the range
of ≧1 and ≦10, advantageously ≧2 and ≦6, and
with more particular advantage ≧3 and ≦5. The pH in this
case may be set using all of the basic compounds that are familiar to the
skilled worker. It is advantageous, however, to use those basic compounds
which are not volatile at the temperatures during drying and/or curing,
such as sodium hydroxide, potassium hydroxide or sodium carbonate, for
example.

[0091]The abovementioned aqueous binders are advantageously suitable for
use as binders for fibrous and granular substrates. With advantage,
therefore, the aqueous binders stated can be used in the production of
shaped articles from fibrous and granular substrates.

[0092]Fibrous and/or granular substrates are familiar to the skilled
worker. Examples include wood chips, wood fibers, cellulose fibers,
textile fibers, plastics fibers, glass fibers, mineral fibers or natural
fibers such as jute, flax, hemp or sisal, but also cork chips or sand,
and also other organic or inorganic, natural and/or synthetic, fibrous
and/or granular compounds whose longest extent, in the case of granular
substrates, is ≦10 mm, preferably ≧5 mm, and more
particularly ≧2 mm. It will be appreciated that the term
"substrate" is also intended to comprise the fiber webs obtainable from
fibers, such as, for example, those known as needled fiber webs. With
more particular advantage the aqueous binder of the invention is suitable
as a formaldehyde-free binder system for the aforementioned fibers and
for fiber webs formed from them.

[0093]The process for producing a shaped article from a fibrous and/or
granular substrate and the aforementioned aqueous binder is
advantageously performed by first impregnating the fibrous and/or
granular substrate with the aqueous binder, bringing the impregnated
substrate, if appropriate, into the desired shape, and subsequently
drying the impregnated substrate and curing it at a temperature
≧130° C.

[0094]The impregnation of the fibrous and/or granular substrates is
generally accomplished by applying the aforementioned aqueous binder
uniformly to the surface of the fibrous and/or granular substrates. The
amount of aqueous binder in this case is chosen such that ≧1 g and
≦100 g, preferably ≧2 g and ≦50 g, and with more
particular preference ≧5 g and ≦30 g of binder, formed from
the sum of polymer A and polyol B (reckoned as solids), are used per 100
g of fibrous and/or granular substrate. The impregnation of the fibrous
and/or granular substrates is familiar to the skilled worker and takes
place, for example, by drenching or by spraying of the fibrous and/or
granular substrates.

[0095]Following impregnation, the fibrous and/or granular substrate is
optionally brought into the desired form, by means, for example, of
introduction into a heatable press or mold. Subsequently the shaped
impregnated fibrous and/or granular substrate is dried and cured in a
manner familiar to the skilled worker.

[0096]Frequently the drying and/or curing of the impregnated fibrous
and/or granular substrate, which has been optionally brought into shape,
takes place in two temperature stages, the drying stage taking place at a
temperature <130° C., preferably ≧20° C. and
≦120° C., and with more particular preference ≧40
and 5100° C., and the curing stage taking place at a temperature
of ≧130° C., preferably ≧150 and ≦250°
C., and with more particular preference ≧180° C. and
≦220° C.

[0097]The drying stage in this case takes place advantageously such that
drying at a temperature ≦100° C. is carried out until the
shaped, impregnated fibrous and/or granular substrate, which frequently
still does not have its ultimate shape (and is referred to as a
semifinished product), has a residual moisture content ≦15%,
preferably ≦12%, and with more particular preference ≦10%
by weight. This residual moisture content is determined by first weighing
the resulting semifinished product at room temperature, then drying it at
130° C. for 2 minutes, and subsequently cooling it and reweighing
it at room temperature. In this case the residual moisture content
corresponds to the difference in weight of the semifinished product
before and after the drying operation, relative to the weight of the
semifinished product before the drying operation, multiplied by a factor
of 100.

[0098]The semifinished product obtained in this way is still deformable
after heating to a temperature ≧100° C., and at that
temperature can be brought into the ultimate shape of the desired shaped
article.

[0099]The subsequent curing stage takes place advantageously such that the
semifinished product is heated at a temperature ≧130° C.
until it has a residual moisture content ≦3%, preferably
≦1%, and with more particular preference ≦0.5% by weight,
the binder curing as a consequence of a chemical esterification reaction.

[0100]Frequently the shaped articles are produced by bringing the
semifinished product into its ultimate shape in a shaping press, in the
aforementioned temperature ranges, and subsequently curing it.

[0101]It will be appreciated, however, that it is also possible for the
drying stage and the curing stage of the shaped articles to take place in
one workstep, in a shaping press, for example.

[0102]The shaped articles obtainable by the process of the invention have
advantageous properties, more particularly an improved tensile strength
in the wet and/or hot state as compared with the prior-art shaped
articles.

[0103]The invention is elucidated with reference to the following
nonlimiting examples.

EXAMPLES

A. Preparation of the Polymer A

Inventive Example 1 (I1)

[0104]A 2 I four-necked flask equipped with an anchor stirrer, reflux
condenser, and two metering devices was charged at 20 to 25° C.
(room temperature) with 200.0 g of methyl ethyl ketone (MEK) and 171.1 g
of maleic anhydride (MAn) under a nitrogen atmosphere. Subsequently the
initial-charge solution was heated to 82° C. with stirring, and,
beginning simultaneously, feed stream 1 was metered in over the course of
5 hours and feed stream 2 over the course of 5.5 hours, both continuously
and with constant volume flows. Thereafter the reaction mixture was
polymerized at the aforementioned temperature for 2 more hours, after
which the polymer solution obtained was cooled to room temperature.

[0110]Subsequently 1000 g of the organic polymer solution obtained were
diluted with 800 g of deionized water, and MEK was distilled off over 5
hours at a temperature of 110-115° C. under atmosphere pressure (1
atm=1.013 bar absolute) by introduction of steam. Thereafter a solids
content of 54% by weight was set by addition of deionized water. The K
value of the polymer A was found to be 19.1, and the weight-average
molecular weight was found to be 13 100 g/mol.

[0111]The solids content was generally determined by drying a sample of
approximately 1 g in a forced-air drying oven at 120° C. for two
hours. Two separate measurements were carried out in each case. The
figures reported in the examples are averages of the two results.

[0112]The K value of the polymer A was determined by the method of
Fikentscher (ISO 1628-1) by means of a 1% strength by weight polymer
solution.

[0114]A 2 I four-necked flask equipped with an anchor stirrer, reflux
condenser, and three metering devices was charged at room temperature
with 200.0 g of MEK and 51.3 g of MAn under a nitrogen atmosphere.
Subsequently the initial-charge solution was heated to 82° C. with
stirring, and, beginning simultaneously, feed stream 1 was metered in
over the course of 3 hours, feed stream 2 over the course of 5 hours, and
feed stream 3 over the course of 5.5 hours, all three continuously and
with constant volume flows. Thereafter the reaction mixture was
polymerized at the aforementioned temperature for 2 more hours, after
which the polymer solution obtained was cooled to room temperature.

Feed Stream 1:

[0115]119.8 g MAn (in melted form)

Feed Stream 2:

[0115][0116]376.0 g AA [0117]96.5 g 1-octene, and [0118]217.0 g MEK

Feed Stream 3:

[0118][0119]42.9 g a 75% strength by weight solution of t-butyl
perpivalate in an aromatic-free hydrocarbon mixture and [0120]183.7 g MEK

[0121]Subsequently 1200 g of the organic polymer solution obtained were
diluted with 700 g of deionized water, and water/MEK was distilled off on
a rotary evaporator at a bath temperature of 80° C. until an
internal pressure of 20 mbar (absolute) had been reached. Thereafter a
solids content of 50% by weight was set by addition of deionized water.
The K value of the polymer A was found to be 15.0, and the weight-average
molecular weight was found to be 11 700 g/mol.

Inventive Example 3 (I3)

[0122]Inventive example 3 was carried out in the same way as for inventive
example 2, but using 343.8 g of AA, 128.7 g of 1-octene, and 217.0 g of
MEK as feed stream 2.

[0123]Deionized water was added to set a solids content of 48.5% by
weight. The K value of the polymer A was found to be 14.3, and the
weight-average molecular weight was found to be 8300 g/mol.

Comparative Example 1 (C1)

[0124]Comparative example 1 was prepared in the same way as for inventive
example 1, but with the total monomer amount and the AA/MAn ratio (2.57)
kept constant, with the inclusion of 181.1 g of MAn in the initial charge
to the polymerization vessel, and with feed stream 1 composed exclusively
of 463.5 g of AA and 217.0 g of MEK.

[0125]Deionized water was added to set a solids content of 42.5% by
weight. The K value of the polymer A was found to be 17.2, and the
weight-average molecular weight was found to be 11 100 g/mol.

Comparative Example 2 (C2)

[0126]Comparative example 2 was prepared in the same way as for inventive
example 2, but with the total monomer amount and the AA/MAn ratio (2.20)
kept constant, with the inclusion of 201.3 g of MAn in the initial charge
to the polymerization vessel, and with feed stream 1 composed exclusively
of 442.3 g of AA and 217.0 g of MEK.

[0127]Deionized water was added to set a solids content of 44.2% by
weight. The K value of the polymer was found to be 16.8, and the
weight-average molecular weight was found to be 15 200 g/mol.

Comparative Example 3 (C3)

[0128]Comparative example 3 was prepared in the same way as for inventive
example 3, but with the total monomer amount and the AA/MAn ratio (2.01)
kept constant, with the inclusion of 213.9 g of MAn in the initial charge
to the polymerization vessel, and with feed stream 1 composed exclusively
of 429.7 g of AA and 217.0 g of MEK.

[0129]Deionized water was added to set a solids content of 42.7% by
weight. The K value of the polymer was found to be 16.7, and the
weight-average molecular weight was found to be 14 900 g/mol.

[0131]The aqueous polymer solutions I1 to 13 and also C1 to C3 obtained in
accordance with the inventive and comparative examples were admixed at
room temperature and with stirring with an amount of triethanolamine
sufficient to make the aqueous solutions comprise 30 parts by weight of
triethanolamine per 100 parts by weight of polymer. Added subsequently to
these solutions, likewise at room temperature and with stirring, was 1
part by weight of 3-aminopropyltriethoxysilane, based on 100 parts by
weight of binder, formed from the amounts of polymer and the
triethanolamine (solid/solid), and the aqueous binder solutions obtained
were diluted with deionized water to a solids content of 25% by weight.
Thereafter the glass fiber webs were passed in longitudinal direction via
a continuous PES sieve belt with a belt running speed of 60 cm per minute
through the aforementioned 25% strength by weight aqueous binder liquors.
Through subsequent suction removal of the aqueous binder, the wet add-on
was set at 48 g/m2 (corresponding to 12 g/m2 binder, reckoned
as solid). The impregnated glass fiber webs obtained in this way were
dried/cured in a Mathis oven, on a plastic net support, either at
180° C. for 2 minutes or at 200° C. for 2 minutes, with the
maximum hot-air flow. After the webs had been cooled to room temperature,
test strips measuring 240×50 mm were cut in the longitudinal
direction of the fiber. The test strips obtained were then stored in a
climate chamber at 23° C. and 50% relative humidity for 24 hours.
The glass fiber web test strips obtained are referred to below, as a
function of the polymer solution used for the aqueous binder, as test
strips I1, I2, I3, C1, C2, and C3.

[0132]Determination of the tensile strength at 23° C.

[0133]The tensile strength was determined on a Zwick-Roell Z005 tensile
testing machine. The test strips I1, I2, I3, C1, C2, and C3 were
introduced vertically into a clamping device such that the free
clamped-in length was 200 mm. Subsequently the clamped-in test strips
were pulled apart in opposite directions at a speed of 25 mm per minute
until the test strips tore. The higher the force needed to tear the test
strips, the better the evaluation of the corresponding tensile strength.
5 measurements were carried out in each case. The figures reported in
Table 1 represent in each case the average of these measurements.

Determination of the Wet Tensile Strength

[0134]The wet tensile strength was determined in the same way as the
tensile strength, at 23° C., with the difference that the
respective test strips were stored in deionized water at 80° C.
for 15 minutes first, and excess water was dabbed off with cotton fabric
prior to measurement. The results obtained are likewise compiled in Table
1.